How to Drain a Hydronic System

boiler system
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  • Beginner
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A hydronic system of boiler heating for the house is one of the most common systems. Although draining it can be time-consuming, it is easy to do.

Step 1 - Empty the System

Emptying the system first requires you to turn off the heating. Initially, you wouldn’t turn off the pump as you require the water to cool down. Each system has an expansion tank. When water is hot it expands and needs to be replenished as it cools down. This tank is usually found in the attic.

Turn off the water that is filling this tank. You will normally find a stop cock located somewhere near. This brings the water in from the mains and by turning it off you will stop the tank from refilling. Allow the water to completely cool down, and then drain the tank by opening the drain cock located on the return pipe to the boiler. Lead the water out of the drain cock with a hose pipe. This will stop your basement from being flooded provided you have properly attached it and placed the end of the hose into an exterior outlet. Once it is drained bleed each of the radiators starting from the highest down to the lowest.

Step 2- Refill the System

Once drained, your system can be refilled by making sure all the drain valves are tightly closed. Reopen the drain cock in the basement and open up the stop cock in the attic to allow the water to start flowing in again. Once the tank is filled, you can then turn the pump and heater back on, and your hydronic system is back working again.